## New features of SISYPHE v6.2

# NEW OPTIONS AND NEW KEY-WORDS

The main new features of this version 6.2 are:

- An improved treatment of mass-balance checking in bedload, both in finite elements and finite volumes options. Accuracy of the machine is now verified.
- An improved treatment of prescribed bedload discharges, with a new keyword.
- A new mass balance subroutine for cohesive sediments, which takes into account the vertical structure of the cohesive sediment bed.
- An update of the % of each class in case of mixed sediments.
- 3 consolidation algorithms, only two in the official version, the third one is in a test case. In order to use those algorithms and specify the right parameters, please refer to the new documentation (cf. report EDF-LNHE H-P73-2012-0289).
- Automatisation of test cases.

## Boundary conditions: imposed transport rates

For bedload: The type of boundary conditions (up to release 6.1) depend on (LIEBOR = 4) and EBOR: zero evolution. It is now possible to prescribe also the transport rate.

New values are used in the BOUNDARY CONDITIONS FILE, that may cause changes of behavior in old cases if not secured. An example of line in this file is given below, with in red the new activated values:

4 5 5 1.E-4 0. 0. 0. 4 0. 0. 0.

LIHBOR LIQBOR Q2BOR LIEBOR EBOR

LIHBOR is actually not used but is now available for users. LIQBOR is the boundary condition on solid discharge (that was before given by user in subroutine conlis, after initialization to KSORT in sisyphe). On liquid boundaries you must now have:

LIQBOR=5 (KENT) and LIEBOR=4 (KSORT) for boundaries with prescribed solid discharge.

LIEBOR=5 (KENT) and LIQBOR=4 (KSORT) for boundaries with prescribed variation of elevation.

Q2BOR is the prescribed solid discharge given at boundary points, and expressed in m2/s, excluding voids. If the keyword PRESCRIBED SOLID DISCHARGES is not given in the parameter file, these values will be taken as such to give QBOR per point, which is in m3/s, excluding voids. When the keyword PRESCRIBED SOLID DISCHARGES is given it supersedes Q2BOR, which is then taken only as a profile.

All these values are meant for the total if there are sediment classes, and in this case they will be distributed to every class with the help of the fractions (array AVAIL), this is done for EBOR and QBOR in CONLIS and may be changed.

For suspended load, concentrations can be imposed on the upstream boundary or imposed, by reading an input concentration file (for time-varying concentrations). The other options available in 6.1 are either to impose constant concentrations on the upstream boundary or to calculate the concentrations assuming equilibrium conditions (if LICBOR = 5).

Note : the type of boundary condition depends on LIEBOR (LICBOR is set equal to LIEBOR). This value is changed depending on the sign U.n in subroutine Diffin.f.

New or modified key-words :

‘PRESCRIBED SOLID DISCHARGES’ (DEBITS SOLIDES IMPOSES)

A sequence of real values separated by semi-columns, one value per liquid boundary. No default value.

Cohesive sediments

New developments include: initialization of cohesive sediment bed layers, consolidation algorithms, a mass balance which takes into account the cohesive sediment bed structure (subroutine bilan-sisyphe-coh.f). The new documentation describes the physical background and numerical discretization.

New or modified key-words

‘ NUMBER OF LAYERS OF THE CONSOLIDATION MODEL’ = NCOUCH_TASS (< 20). Default value : NCOUCH_TASS= 1

‘NUMBER OF BED LOAD MODEL LAYERS’ = NOMBLAY (< 20). Default value : NOMBLAY= 2

Both keywords should be merged, only NOMBLAY is used in the fortran code. In lecdon_sisyphe.f NOMBAY = MAX(NOMBLAY, NCOUCH_TASS). The maximum number of layers is fixed up to NLAYMAX= 20.

Both keywords do not have the same default value. In order to have a uniform cohesive bed, it is so far necessary to specify both keywords to 1.

‘ NUMBER OF LAYERS OF THE CONSOLIDATION MODEL’ =1

‘NUMBER OF BED LOAD MODEL LAYERS’ = 1

If not, it will take the maximum default value : 2

‘ NUMBER OF LAYERS OF THE CONSOLIDATION MODEL’ = NOMBLAY (< 20)

‘ MUD CONCENTRATION PER LAYER’ : CONC_VASE (J=1, NOMBLAY)

Modified subroutines

User Subroutine ‘suspension_compo_coh.f is a new subroutine to initiaze the cohésive sediment bed – thicknesses and concentrations.

This subroutine is called by Init_mixte.f and used for cohesive sediments only as well as to mixed (sand/mud) sediments

ES(IPOIN, JLAYER) is the total bed thickness

CONC(IPOIN,JLAYER) is the mass concentration per point and per layer (Kg/m3).

By default it is constant per layer and specified by the key-word.

New numerical schemes for consolidation

Three models are available in 6.2 (the third one is still only in a test case), but due to unstabilities when running the morphodynamics model, it is not yet available in the final version. This third version is similar to the consolidation implemented in Sedi 3D.

The consolidation algorithm (model 2) is based on the Gibson’s theory. The Gibson equation is based on the Darcy’s law (sedimentation ) and Terzaghi’s law for consolidation.

Where e is the void ratio. The bed permeability and k(C) and effective stress ?’(C), are the main closure equations which are directly specified in tassement2.f

In order to solve this equation, two different regimes are distinguished

Sedimentation regime : C<Cgel

The effective stress term (last term) is neglected.

Consolidation regime : C>Cgel

Only the effective stress is retained (advection neglected)

Key words of the consolidation algorithm (Model 2)

‘COHESIVE SEDIMENT’ = YES

‘MUD CONSOLIDATION’ = YES

‘ CONSOLIDATION MODEL’ = 2

‘ GEL CONCENTRATION’ = CONC_GEL

‘ MAXIMUM CONCENTRATION’ = CONC_MAX

‘ PERMEABILITY COEFFICIENT’ = COEF_N